Synergistic Dual Modulation of Quinoxaline Acceptors via Core‐Fluorination and Side‐Chain Engineering for High‐Efficiency Organic Solar Cells

ABSTRACT While fluorination and alkyl chain modifications are recognized as effective strategies for regulating the packing behavior of non‐fullerene acceptor (NFA) molecules, their specific impacts on dielectric properties and associated energy losses in organic solar cells (OSCs) remain unclear, posing a constraint on further efficiency enhancements. To address this gap, it is designed and synthesized a series of NFAs with systematically varied quinoxaline fluorination degrees and alkyl chain lengths, aiming to elucidate the structure‐property relationship whereby molecular architecture governs dielectric characteristics, directs molecular packing, and ultimately dictates device performance. This findings demonstrated that both increased core fluorination and extended alkyl side chains enhance the dielectric properties of NFAs while concurrently reducing the free volume within the molecular packing. Notably, the C ₁₂ BQ‐o8F molecule—featuring octa‐fluorination and a 2‐butyloctyl side chain—achieved the highest dielectric constant (2.42) and exhibited dense in‐plane molecular packing (19.50 Å), facilitating ultrafast hole transfer and markedly reducing voltage loss (0.491 eV). When incorporated as a guest acceptor into the PM6:BTP‐eC9 binary host, the resulting ternary device attained an efficiency of 19.52%. This work elucidates the critical interplay between core fluorination and side‐chain engineering in modulating dielectric properties, offering a molecular design pathway toward low‐loss, high‐efficiency OSCs.